elc_popup.c: make popup handle general content set.
elc_popup.c: make popup handle general content set.

Currently application can use "default", "title,icon", "button{n}" parts for content_set but this patch allows more flexible usage of content_set.

tasn/elementary,rvandegrift/elementary,FlorentRevest/Elementary,tasn/elementary,tasn/elementary,FlorentRevest/Elementary,tasn/elementary,tasn/elementary,rvandegrift/elementary,FlorentRevest/Elementary,rvandegrift/elementary,FlorentRevest/Elementary,rvandegrift/elementary